| Records |
| Author |
Kumar, Sushil; Chan, Chun Wang I.; Hu, Qing; Reno, John L. |
| Title |
A 1.8-THz quantum cascade laser operating significantly above the temperature of hw/k |
Type |
Journal Article |
| Year |
2011 |
Publication |
Nature Physics |
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| Volume |
7 |
Issue |
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Pages |
166-171 |
| Keywords |
QCL, 2 mW at 155 K and 1.8 THz |
| Abstract |
Several competing technologies continue to advance the field of terahertz science; of particular importance has been the development of a terahertz semiconductor quantum cascade laser (QCL), which is arguably the only solid-state terahertz source with average optical power levels of much greater than a milliwatt. Terahertz QCLs are required to be cryogenically cooled and improvement of their temperature performance is the single most important research goal in the field. Thus far, their maximum operating temperature has been empirically limited to ~planckω/kB, a largely inexplicable trend that has bred speculation that a room-temperature terahertz QCL may not be possible in materials used at present. Here, we argue that this behaviour is an indirect consequence of the resonant-tunnelling injection mechanism employed in all previously reported terahertz QCLs. We demonstrate a new scattering-assisted injection scheme to surpass this limit for a 1.8-THz QCL that operates up to ~1.9planckω/kB (163 K). Peak optical power in excess of 2 mW was detected from the laser at 155 K. This development should make QCL technology attractive for applications below 2 THz, and initiate new design strategies for realizing a room-temperature terahertz semiconductor laser. |
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631 |
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Beck, M.; Klammer, M.; Lang, S.; Leiderer, P.; Kabanov, V. V.; Gol’tsman, G. N.; Demsar, J. |
| Title |
Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy |
Type |
Miscellaneous |
| Year |
2011 |
Publication |
arXiv |
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| Keywords |
NbN thin film, energy gap dynamics |
| Abstract |
Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, \lambda = 1.1 +/- 0.1, which is in excellent agreement with theoretical estimates. |
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Duplicated as 641 |
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no |
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1388 |
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Shangina, E. L.; Smirnov, K. V.; Morozov, D. V.; Kovalyuk, V. V.; Goltsman, G. N.; Verevkin, A. A.; Toropov, A. I.; Mauskopf, P. |
| Title |
Concentration dependence of energy relaxation time in AlGaAs/GaAs heterojunctions: direct measurements |
Type |
Journal Article |
| Year |
2011 |
Publication |
Semicond. Sci. Technol. |
Abbreviated Journal |
Semicond. Sci. Technol. |
| Volume |
26 |
Issue |
2 |
Pages |
025013 |
| Keywords |
AlGaAs/GaAs heterojunctions |
| Abstract |
We present measurements of the energy relaxation time, τε, of electrons in a single heterojunction in a quasi-equilibrium state using microwave time-resolved spectroscopy at 4.2 K. We find the relaxation time has a power-law dependence on the carrier density of the two-dimensional electron gas, τε∝nγs with γ = 0.40 ± 0.02 for values of the carrier density, ns, from 1.6 × 1011 to 6.6 × 1011cm−2. The results are in good agreement with predictions taking into account the scattering of the carriers by both piezoelectric and deformation potential acoustic phonons. We compare these results with indirect measurements of the energy relaxation time from energy loss measurements involving Joule heating of the electron gas. |
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0268-1242 |
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1215 |
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Курочкин, Юрий Владимирович |
| Title |
Методы повышения пропускной способности квантовой криптографии |
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Manuscript |
| Year |
2011 |
Publication |
МФТИ |
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| Keywords |
quantum cryptography |
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Ph.D. thesis |
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no |
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762 |
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Kawakami, A; Saito, S.; Hyodo, M. |
| Title |
Fabrication of nano-antennas for superconducting Infrared detectors |
Type |
Journal Article |
| Year |
2011 |
Publication |
IEEE Trans. Appl. Supercond. |
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| Volume |
21 |
Issue |
3 |
Pages |
632-635 |
| Keywords |
optical antennas, NbN/MgO/NbN/TiN/Al HEB, dipole antennas, IR, infrared |
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To improve the response performance of superconducting infrared detectors, we have developed a fabrication process for nano-antennas. A nano-antenna consists of a dipole antenna, and a superconducting thin film strip placed in the antenna's center. By measuring the transition temperature of the superconducting strips, we confirmed that their superconductivity maintained a good condition after the nano-antenna fabrication process. We also evaluated nano-antenna characteristics using Fourier transform infrared spectroscopy. The evaluated antenna length and width were respectively set at around 2400 nm and 400 nm, and the antennas were placed at intervals of several micrometers around the area of 1 mm2 . In an evaluation of spectral transmission characteristics, clear absorption caused by antenna effects was observed at around 1400 cm-1. High polarization dependencies were also observed. |
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no |
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761 |
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Sprengers, J.P.; Gaggero, A.; Sahin, D.; Nejad, S. Jahanmiri; Mattioli, F.; Leoni, R.; Beetz, J.; Lermer, M.; Kamp, M.; Höfling, S.; Sanjines, R.; Fiore A. |
| Title |
Waveguide single-photon detectors for integrated quantum photonic circuits |
Type |
Conference Article |
| Year |
2011 |
Publication |
arXiv |
Abbreviated Journal |
arXiv |
| Volume |
1108.5107 |
Issue |
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Pages |
1-11 |
| Keywords |
optical waveguides, waveguide SSPD |
| Abstract |
The generation, manipulation and detection of quantum bits (qubits) encoded on single photons is at the heart of quantum communication and optical quantum information processing. The combination of single-photon sources, passive optical circuits and single-photon detectors enables quantum repeaters and qubit amplifiers, and also forms the basis of all-optical quantum gates and of linear-optics quantum computing. However, the monolithic integration of sources, waveguides and detectors on the same chip, as needed for scaling to meaningful number of qubits, is very challenging, and previous work on quantum photonic circuits has used external sources and detectors. Here we propose an approach to a fully-integrated quantum photonic circuit on a semiconductor chip, and demonstrate a key component of such circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (20%) at telecom wavelengths, high timing accuracy (60 ps), response time in the ns range, and are fully compatible with the integration of single-photon sources, passive networks and modulators. |
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846 |
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Sprengers, J. P.; Gaggero, A.; Sahin, D.; Jahanmirinejad, S.; Frucci, G.; Mattioli, F.; Leoni, R.; Beetz, J.; Lermer, M.; Kamp, M.; Höfling, S.; Sanjines, R.; Fiore A. |
| Title |
Waveguide superconducting single-photon detectors for integrated quantum photonic circuits |
Type |
Journal Article |
| Year |
2011 |
Publication |
Applied Physics Letters |
Abbreviated Journal |
Appl. Phys. Lett. |
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99 |
Issue |
18 |
Pages |
181110(1-3) |
| Keywords |
optical waveguides, waveguide SSPD |
| Abstract |
The monolithic integration of single-photon sources, passive optical circuits, and single-photon detectors enables complex and scalable quantum photonic integrated circuits, for application in linear-optics quantum computing and quantum communications. Here, we demonstrate a key component of such a circuit, a waveguide single-photon detector. Our detectors, based on superconducting nanowires on GaAs ridge waveguides, provide high efficiency (~0%) at telecom wavelengths, high timing accuracy (~0 ps), and response time in the ns range and are fully compatible with the integration of single-photon sources, passive networks, and modulators. |
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847 |
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Lee, B. G.; Assefa, S.; Green, W. M. J.; Min Yang; Schow, C. L.; Jahnes, C. V.; Sheng Zhang; Singer, J.; Kopp, V. I.; Kash, J. A.; Vlasov, Y. A. |
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Multichannel high-bandwidth coupling of ultradense silicon photonic waveguide array to standard-pitch fiber array |
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Journal Article |
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2011 |
Publication |
J. Lightwave Technol. |
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29 |
Issue |
4 |
Pages |
475-482 |
| Keywords |
optical waveguides, from chiralphotonics |
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A multichannel tapered coupler interfacing standard 250-μm-pitch low-numerical-aperture (NA) polarization-maintaining fiber arrays with ultradense 20- μm-pitch high-NA silicon waveguides is designed and fabricated. The coupler is based on an array of 12 dual-core glass waveguides on 250-μ m pitch that are tapered to a 20- μm pitch, simultaneously providing both pitch and spot-size conversion. At the wide end, the inner core matches the NA and mode profile of standard single-mode fiber. When drawn and tapered, the inner core “vanishes†and the outer core, surrounded by the clad, matches the NA and mode profile of the on-chip photonic waveguide. Ultradense high-efficiency coupling to an array of Si photonic waveguides is demonstrated using a 12-channel polarization-maintaining-fiber pigtailed tapered coupler. Coupling to Si waveguides is facilitated using SiON spot-size converters integrated into the Si photonic IC to provide 2-3-μm mode field diameters compatible with the tapered coupler. The tapered coupler achieves <; 1 dB coupling losses to photonic waveguides. Furthermore, eight-channel coupling is shown with less than -35 dB crosstalk between channels. Finally, a 640-Gb/s wavelength-division-multiplexing signal is coupled into four waveguides occupying 80 μm of chip edge, providing 160-Gb/s per-channel bandwidths. |
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849 |
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ГОСТ 3.1102-2011. ЕСТД. Стадии разработки и виды документов. Общие положения |
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Book Whole |
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2011 |
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gost, detproj |
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864 |
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Galeazzi, Massimiliano |
| Title |
Fundamental noise processes in TES devices |
Type |
Journal Article |
| Year |
2011 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
| Volume |
21 |
Issue |
3 |
Pages |
267-271 |
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TES, Johnson noise, phonon noise, excess noise, flux-flow noise, thermal fluctuation noise |
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Microcalorimeters and bolometers are noise-limited devices, therefore, a proper understanding of all noise sources is essential to predict and interpret their performance. In this paper, I review the fundamental noise processes contributing to Transition Edge Sensor (TES) microcalorimeters and bolometers and their effect on device performance. In particular, I will start with a simple, monolithic device model, moving to a more complex one involving discrete components, to finally move to today's more realistic, comprehensive model. In addition to the basic noise contribution (equilibrium Johnson noise and phonon noise), TES are significantly affected by extra noise, which is commonly referred to as excess noise. Different fundamental processes have been proposed and investigated to explain the origin of this excess noise, in particular near equilibrium non-linear Johnson noise, flux-flow noise, and internal thermal fluctuation noise. Experimental evidence shows that all three processes are real and contribute, at different levels, to the TES noise, although different processes become important at different regimes. It is therefore time to discard the term “excess noise” and consider these terms part of the “fundamental noise processes” instead. |
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Recommended by Klapwijk |
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914 |
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